The present invention relates to a method for converting harmful polychlorinated biphenyl oil (PCB) into a resource, whereby polychlorinated biphenyl oil is regenerated into a resource useful as a raw material, an agent for decomposing polychlorinated biphenyl oil, and a reclaimed material.
Polychlorinated biphenyl oil (hereunder, PCB) exhibits different properties depending on the number and positions of chlorine atoms in the biphenyl, but generally has excellent physical properties and is chemically stable, so that it is used as a heating medium, an insulating oil or the like.
However, PCBs decompose slowly when incorporated into the body, and exhibit toxicity as they are accumulated over long periods. While PCBs are not currently produced, they were once widely used in the past as electrical insulating oil for transistors and other devices, and therefore it is expected in the future that activity will be directed toward collection and waste disposal of established devices in which PCBs have been used, as well as treatment, collection and disposal of PCBs that have flowed out into the environment.
A typical disposal method for PCBs is incineration. Not only PCBs but also many other harmful chemical substances can be decomposed and rendered harmless by incineration. However, incineration disposal often produces new harmful substances such as dioxins during the incineration disposal process, and although efforts are being made to establish high-temperature combustion treatment techniques, at the current time in Japan, no incineration treatment facility sites are being realized due to concerns about their influence on the surrounding environments.
As regards techniques for rendering PCBs harmless, for example, a xe2x80x9cchemical extraction decomposition methodxe2x80x9d had been introduced on an Internet web site of the Tokyo Electric Power Company (Press Release: xe2x80x9cDevelopment of Treatment Techniques for Rendering PCBs Harmlessxe2x80x9d, Dec. 2, 1996) (Prior Art Example 1). The method of Prior Art Example 1 is a method whereby a solvent is added to an insulating oil containing PCBs and the chlorine (Cl) in the PCBs is activated and reacted with sodium hydroxide (NaOH) to convert the PCBs to completely harmless salt (NaCl) and biphenyl.
It is emphasized that the effects provided by this method are that:
the treatment can be carried out in completely sealed facilities, wherein there is absolutely no effect on the surrounding environment, and high decomposition performance is ensured that allows its application on a practical level for the first time, for PCBs in insulating oils either at low concentration (about 0.02%) or high concentration (about 70%),
the chemical reaction is a safe treatment method since it is carried out under conditions of about 200xc2x0 C. and ordinary pressure,
there is no generation of harmful substances during the reaction, only harmless insulating oils and salt remain after the treatment, and they can be reused as the fuel oil or regenerated insulating oil.
This is indeed considered to be a technique based on an excellent concept from the standpoint of making possible not only treatment to render PCBs harmless, but also reuse the reaction products as resources. The full concept of the xe2x80x9cchemical extraction decomposition methodxe2x80x9d referred to above is not obvious just from the disclosed contents mentioned above, but it is essentially believed to be a method for rendering PCB harmless by chemical reaction alone.
There is a general problem in that with a chemical reaction alone it is not always possible to guarantee that 100% chemical conversion is occurring. For example, even if the amounts of residual PCB satisfy safety standards, the problem of residual PCBs has not been solved.
As a method for solving such problems, a method for making PCBs harmless has been proposed (refer to U.S. Pat. No. 5,744,689), in which PCB oil is converted to harmless chlorine compounds such as calcium chloride, magnesium chloride, etc., by utilizing a decomposing action and heat-generating reaction of Ca using a treating agent containing calcium oxide and at least silicon dioxide and magnesium. However, where the above-described method is employed, not only are the remaining amounts of PCBs made uneven even after the treatment, but it also has been found that, even if PCBs are initially decomposed to harmless chlorine compounds, the decomposed substances are restored to PCBs again. Although the reason why such a phenomenon occurs is not necessarily clear, it is considered that the decomposed substances of PCBs are formed based on partially unstable bonding. Also, there is another problem in that calcium oxide (quick lime), which is the main element of the decomposing agent, absorbs humidity in the atmospheric air to cause its quality to be lowered, and no expected decomposing action can be carried out.
It is therefore an object of the invention to provide a method for converting harmful polychlorinated biphenyl oil (PCB oil) into a resource, by which polychlorinated biphenyl oil is regenerated into a resource useful as a raw material without being restored to PCBs again after PCBs are initially decomposed to be harmless, an agent for decomposing polychlorinated biphenyl oil, and a reclaimed material regenerated by said method for converting harmful polychlorinated biphenyl oil.
In order to achieve this object, the method for converting polychlorinated biphenyl oil into a resource, according to the invention, is a method for converting polychlorinated biphenyl oil into a resource by a chemical decomposition treatment, a pelletizing treatment and a thermal decomposition treatment, wherein
the chemical decomposition treatment is a treatment in which a decomposing action of CaO and far-infrared rays emitted by quartz porphyry act on PCB oil, and the PCB oil is chemically converted to produce a powder containing a metal salt,
the pelletizing treatment is a treatment in which powder produced by the chemical decomposing treatment is hardened into pellets, and
the thermal decomposition treatment is a treatment in which the pellets are heat treated with glass cullet at a temperature above the thermal decomposition temperature of the polychlorinated biphenyl for molten integration, and the molten integrated slag is cooled to be made into a solid to be reused as a resource.
The slag obtained by the thermal decomposition treatment is cooled for reuse as a solid.
Also, the chemical decomposing treatment includes a process of decomposing PCBs by causing heat, which is caused by an exothermic reaction of CaO, to act on quartz porphyry and irradiating far-infrared rays from the quartz porphyry under a condition that the quartz porphyry is heated above 200xc2x0 C.
Also, the chemical decomposing treatment is a treatment in which minus ions radiated from quartz porphyry are acted on PCB oil and the PCB oil is further decomposed by its reduction action.
The thermal decomposition treatment is also a treatment for thermal decomposition of the PCB oil component possibly remaining in the powder produced from the chemical decomposition treatment.
The thermal decomposition treatment is carried out in a melting furnace with coke as the fuel, and the pellets produced by the pelletizing treatment also serve to adjust the degree of basicity for loading into the melting furnace.
The invention still further provides a method for converting PCB oil into a resource by chemical decomposition treatment, pelletizing treatment and thermal decomposition treatment, wherein
the chemical decomposition treatment is a treatment in which the PCB oil is chemically converted into powder containing a metal salt, to protect the working environment from contamination by PCB oil during the thermal decomposition treatment,
the pelletizing treatment is a treatment in which the powder produced by the chemical decomposition treatment is worked into pellets as pretreatment to the thermal decomposition treatment, in order to prevent the powder from blowing away and facilitate its handling during the thermal decomposition treatment, and
the thermal decomposition treatment is a treatment in which the pellets obtained by the pelletizing treatment are loaded together with glass cullet into a melting furnace with coke as the fuel and both are melted in the melting furnace at a temperature above the thermal decomposition temperature of the PCBs, so that the pellets are melted and integrated with the glass to obtain slag which is then cooled for reuse as a solid.
A decomposing agent of PCB oil according to the invention is a decomposing agent of PCB oil, which contains calcium oxide powder whose surface is coated with a vegetable oil, and quartz porphyry powder.
Also, a reclaimed material that is obtained by the method for making PCB oil into resources is a slag that is obtained by the thermal decomposition treatment and is a radiator of far-infrared rays.
The invention renders PCB oil harmless by a two-stage treatment process and provides by-products that can be utilized as renewed resources. The pretreatment comprises chemical decomposition treatment and pelletizing treatment, while the post-treatment consists of thermal decomposition treatment.
The chemical decomposition treatment is a treatment in which the PCB oil is chemically converted to produce powder containing a metal salt by applying a decomposition action and an exothermic reaction of CaO to PCB oil, and acting far-infrared rays emitted by quartz porphyry onto the PCB oil, thus preventing contamination of the post-treatment working environment by PCB oil, while the pelletizing treatment of the produced powder prevents said powder from being blown into the environment during the thermal decomposition treatment and further facilitates handling.
The post-treatment is a treatment in which the pellets are thermally decomposed and undergo molten integration with the glass cullet. The slag produced by molten integration of the pellets and glass cullet is cooled to give a lustrous granite-like solid. The solid is a radiator of far-infrared rays and can be reused as a resource by pulverizing it or cutting it into a desired shape.